The present invention relates to thin film magnetic devices having perpendicular anisotropy.
Magnetic devices, such as thin film recording heads, whether read, read/write, or write, are designed to have particular magnetic orientations, or domains, within the active regions of the device material. The static state of each of these domains can be configured as desired, by control of the manufacturing process. Performance is critically linked to domain formation, and, therefore, control can be exerted over device performance by controlling domain formation.
Conduction of flux, such as in a thin film magnetic head, is achieved by two mechanisms: domain wall motion and domain rotation. Domain wall motion results in flux being transmitted through a thin film head along the walls of a domain, or domains, the flux spreading out along the domain walls as the flux seeks to return to equilibrium. However, while domain wall motion facilitates conduction of flux at low frequencies, it is a poor vehicle for conduction of flux at high frequencies. Furthermore, defects in the material in a magnetic head can be the source of Barkhausen noise during conduction of flux by wall motion as the flux is perturbed by these defects. Such noise can result in erroneous readings of recorded data.
Conduction of flux by domain rotation may be achieved by configuring a series of neighboring domains axially aligned along parallel axes, where flux impinged upon the first domain at a given angle will cause the magnetization of that domain to rotate from its static orientation by that angle radially into and impinging upon the neighboring domain. Such rotation can be transmitted in a like manner along an axis of flux transmission by each neighboring domain of the series. Hence, flux can be conducted in the pole and through the yoke of a thin film head in a series of domain rotations.
The yoke enables conduction of flux through a transducer which produces electrical signals proportional to flux levels or the rate of change of flux. Where the yoke reluctance is high, a significant amount of flux will bypass the transducer, and thus the device output will be reduced.
Certain prior art devices, such as thin film heads, are commonly produced having an anisotropy (at rest domain orientation) parallel to the plane of the substrate and transverse to the signal flux axis. In heads of this type, as track width gets smaller (with the push for higher track density), the region of transverse magnetization, which can transmit flux by rotation, shrinks toward zero. This results from edge domains (longitudinally oriented flux closure regions) dominating the flux path and preventing conduction by rotation. The head will therefore exhibit high reluctance at high frequencies.
A further artifact in conventional recording heads having the above orientation is that even where flux is conducted by rotation, the flux cannot substantially spread as it travels longitudinally from the pole tip through the yoke, since domain rotation can conduct flux efficiently only in the in-plane longitudinal direction in such devices, the other available direction being out-of-plane and of high reluctance.
Further discussion of flux conduction mechanisms will be found in a copending application entitled: Flux Spreading Thin Film Magnetic Devices, U.S. Ser. 07/227,808, No. filed Aug. 3, 1988, now U.S. Pat. No. 5,089,334, and is incorporated herein by reference.